4. COCOMO – HEURISTIC ESTIMATION TECHNIQUE.pptx

software engineering

1. COCOMO – Heuristic estimation technique COCOMO – COnstructive COst estimation MOdel This model was proposed by Boehm, 1981 . He postulated that any software development project can be classified into any one of the following three categories based on the development complexity, they are Organic Semidetached Embedded

2. Cont.. It is not only classified by the characteristic of the product but also by the development team and development environment . The three product classes correspond to application, utility and system programs Data processing program consider as application programs Complier, linker, etc., are Utility program Real time system and operating system etc., are system program

3. Cont.. Utility programs are roughly three times as difficult to write as application program System program are roughly three times as difficult as utility program

4. Cont.. 1.organic: It is organic If the project deals with developing a well understood application program  The size of the development team is reasonably small The team members are experienced in developing similar types of projects

5. Cont.. 2.semidetached: It is semidetached if the developing team consists of mixture of experienced and inexperienced staff Team member may have limited experience on related systems but may be unfamiliar with some aspects of the system being developed

6. Cont.. 3.embedded: It is embedded if the software being developed is strongly coupled to complex hardware

7. Cont.. Boehm provides different sets of expressions to predict the effort and development time from the size estimation given in KLOC (kilo Lines of Source Code ). Open person-month is the effort an individual can typically put in a month. That effort estimation is expressed in units of person-months (PM). The person month unit indicates the work done by one person working on the project for one month.

8. Cont.. Effort estimation of 100PM does not imply that 100persons should work for one month, it imply that 1 person should be employed for 100 months. The number personal working on the project usually increases and decreases.

9. Cont.. Software cost estimation should be done through three stages: Basic COCOMO Model Intermediate COCOMO Complete COCOMO.

10. Basic COCOMO Model The basic COCOMO model gives an approximate estimate of the project parameters. Expression of basic COCOMO model, Effort =a 1 x (KLOC) a2 PM Tdev= b 1 x (Effort) b2 Months Where, KLOC is estimated size in Kilo Lines of Code. a1,a2,b1,b2 are constants for each category of software products. Tdev is the estimated time to develop the software, expressed in months. Effort is total effort required to develop the software product in PM

11. Cont.. Estimation of development effort Organic: effort = 2.4(KLOC) 1.05 PM Semidetached: effort = 3.0(KLOC) 1.12 PM Embedded: effort= 3.6(KLOC) 1.20 PM Estimation of development time Organic: Tdev= 2.5(Effort) 0.38 Months Semidetached: Tdev =2.5(Effort) 0.35 Months Embedded: Tdev =2.5(Effort) 0.32 Months

12. Cont.. If team tries to develop the product in at time shorter than the estimated time than cost will increase rapidly If the team complete the project over a longer period of time than that estimated, then there is almost no decrease in the estimated cost value.

13. Example Assume that the size of an organic type software product has been estimated to be 32,000 lines of source code . Assume that the average salary of a software developer is Rs. 15,000 per month. Determine the effort required to develop the software product, the nominal development time, and the cost to develop the product . From the basic COCOMO estimation, Formula for organic software: Effort = 2.4 × (32) 1.05 = 91PM = 2.4 X 38.0546 =91.33 Nominal development time = 2.5 × (91) 0.38 = 14 months = 2.5 X 5.55182 = 13.879 Staff cost required to develop the product = 91 × Rs. 15, 000 = Rs.1,365,000